Reinforced ignition tube



Aug. 20, 1968 s. w. ALDERFER REINFORCED IGNITION TUBE Filed Jan. 3, 196735/ FIG. 3

FIG.4 -53 INVENTOR. STERLING W. ALDERFER FIG 6 ATTORNEYS United StatesPatent 3,397,639 REINFORCED IGNITION TUBE Sterling W. Alderfer, Akron,Ohio, assignor to Sterling Alderfer Company, Akron, Ohio, a corporationof Ohio Filed Jan. 3, 1967, Ser. No. 606,970 5 Claims. (Cl. 102-70)ABSTRACT OF THE DISCLOSURE A method for making and a specificconstruction of a munitions ignition tube. A complet-e ignition tube isa composite of straight and belled, tubular sections of rigid urethanefoam reinforced, in proximity to their radially outer surface with asleeve of diagonally woven strands of polyester filaments. The sleeve isinserted in the mold and axially compressed so that it radially expandsagainst the mold wall. The foam is rigidified to a desired wallthickness with the sleeve thus positioned.

Background of the invention As is being poignantly demonstrated duringthe armed conflicts in various spots around the world, it is too costly,inconvenient and in many situations highly undesirable for fieldartillery to use cartridge-like ammunition. A cartridge has the printer,propellant and projectile all contained within a shell. Shells areusually made from a high grade brass so that it has sufficientmalleability to withstand the severe mechanical deformation incident tothe shaping of the shell. Not only is the brass itself expensive but sois the cost of fabricating the shell therefrom. Moreover, after thecartridge has been fired the empty shell remains.

This non-expendability of the shell has been found to be mostundesirable, particularly for mobile artillery units. The fired shell isexcess baggage for the artillery crew, and yet, if it is discarded, itleaves a permanent cairn by which movements of the artillery crew can betracked. Accordingly, the practice has been adopted to substitute dualcomponentsi.e., a cartridge sack and a separate projectilefor theunitary cartridges previously used with small and medium sized mobileartillery pieces.

The cartridge sack is a bag filled with propellant; an ignition tubebeing buried in the propellant. The ignition tube holds a powderignition charge and primer which, in turn, ignite the propellant.Although it is permissible for the powder charge to ignite ratherrapidly upon explosion of the primer, the direction in which, and therate at which, the propellant burns is quite critical. Accordingly, theignition tube is carefully perforated and specifically located withinthe cartridge sack so that the propellant is ignited to burn generallyfrom the front to the rear.

Coupled with the requirement for controlled ignition, the cartridge sackmust be completely consumed within the barrel of the artillery piece. Ifany residue in the form of a hard ash remains on the interior of thebarrel it can jam the insertion of the subsequent projectile.

An ignition tube made from rigid polyurethane foam has been foundcapable of controlling the ignition of the propellant and is consumedupon ignition. However, such tubes have been too frangible to permit anyrough handling of the cartridge sack. For example, when the cartridgesacks are parachuted to the artillery teams, the ignition tubes havebroken on landing. The danger can be insidious in that the ignition ofthe propellant by a broken tube may be improper only to the degree thatthe range of the projectile is erratic, or, more unfortunately, thebroken tube can cause the propellant to explode, rather than ignite, andthereby blow the breach or cause permanent damage to the barrel.

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Many attempts have been made to reinforce the polyurethane ignitiontubes, but none have been satisfactory. With the straight tube segmentsexperimentation discloses that the reinforcement is effective only whenit lies contiguously to the radially outer wall. To adapt this teachingto a belled tube has not, however, heretofore been practical.

Summary of the invention It is therefore an object of the presentinvention to provide an ignition tube for a cartridge sack whichincorporates a reinforcement adjacent the radially outer surfacethereof, irrespective of whether or not the tube is straight or belled.

It is another object of the present invention to provide a reinforcedignition tube, as above, which leaves no residual deposits of hard ashon the interior of the barrel.

It is a further object of the present invention to provide an ignitiontube, as above, which will afford controlled ignition of the propellanteven after the cartridge sack has been roughly handled.

These and other objects of the present invention, as well as theadvantages thereof over existing and prior art forms, will be apparentin view of the following detailed description of the attached drawingsand are accomplished by means hereinafter described and claimed.

In general, an ignition tube embodying the concept of the presentinvention is formed from one or more sections of a hollow, generallytubular rigid foam. A reinforcing sleeve is encased within the foam injuxtaposition with the radially outer surface of the tube, even when theradially outer surface of the tube is of progressively varied diameter.

The sleeve itself is preferably woven from polyester strands of twofilaments each. The strands are oriented helically of both right andleft hand lay; the strands of opposite lay being interwoven so that thediameter of the sleeve increases or decreases, respectively, upon axialcompression or elongation of the sleeve.

The increase in diametric dimension upon axial compression allows thesleeve to conform most closely to the outer surface of even a belledtube by simply compressing the sleeve within the cavity of the moldwhich forms the tube before the foam hardens in the mold.

One preferred embodiment of the subject ignition tube, together with themethod by which such a tube is made, are shown by way of example in theaccompanying drawings and are described in detail without attempting toshow all of the various forms and modifications in which the inventionmight be embodied; the invention being'measured by the appended claimsand not by the details of the specification.

Description of the drawings FIG. 1 is a perspective view, partially cutaway, of a cartridge sack incorporating an ignition tube embodying theconcept of the present invention;

FIG. 2 is a schematic side elevation, partly in section, of an artillerypiece with the cartridge sack of FIG. 1 received in the chamber thereof;

FIG. 3 is an enlarged side elevation, partly in section, of a belledtube segment and a portion of a cylindrical segment;

FIG. 4 is a further enlarged side elevation of a reinforcing sleevedepicting the weave thereof in greater detail;

FIG. 5 is a longitudinal section of a mold adapted for making a belledignition tube segment with a cylindrical section of reinforcing sleevereceived therein; and,

FIG. 6 is a view similar to FIG. 5 depicting the sleeve in juxtapositionto the wall of the mold cavity and with the core positioned therein.

Description of the preferred embodiment Referring more particularly tothe drawings, an ignition tube embodying the concept of the presentinvention is indicated generally by the numeral 10. As is shown in theFIG. 1 representation, the ignition tube is buried in the propellantcharge 11 contained within a cloth bag 12. Interiorly of the ignitiontube 10 is the ignition charge 13 which is fired by the primer 14.

The arrangement of the primer 14, ignition charge 13, ignition tube 10and propellant charge 11 are contained within the cloth bag 12 which isitself secured in a generally cylindrical shape by longitudinal bindings15 and 16 and the spaced, circumferential bindings 18 and 19. Thisentire combination is the cartridge sack 20.

The cartridge sack 20 is a self-contained unit which may be stored andtransported independently of the projectile until it is received withinthe chamber of the artillery piece. As shown in the schematicrepresentation of the mobile artillery piece 21 in FIG. 2, the cartridgesack 20 is positioned within the chamber 22 immediately behind theprojectile 23. In order to prevent blowing of the breach 24 thepropellant charge must burn at a controlled rate so that the resultinggases can overcome the static inertia of the projectile 23 and start itmoving forwardly through the barrel 25 without building up excessivechamber pressures. This controlled burning rate is also critical to theaccuracy of the artillery piece 21. As such it has been found highlydesirable to construct the ignition tube 10 from three segments: aIearmost, belled and imperforate segment 28; a middle, cylindrical,perforate segment 29 and a forward, belled, perforate segment 30.

The position and number of the perforations 31 through the walls of themiddle and forward segments 29 and 30, respectively, have been carefullyworked out, in conjunction with the construction and characteristics ofthe particular propellant used, so that the controlled ignition, orburning, thereof is accomplished. These details do not form a part ofthe present invention and will, therefore, not be further described.

Reference is made to the criticality of controlled ignition only so itwill become manifestly apparent that the integrity of the ignition tube10 must be maintained irrespective of Whether the cartridge sack 20 isgently or roughly handled. The quest for a satisfactory way by which toreinforce ignition tubes so that they are capable of withstandingair-drops has been fruitless prior to the subject invention.

Referring to FIG. 3, it can be seen that the rigid foam 32 forms thesubstance, or body, of the tube and is reinforced by a sleeve 33 encasedwithin the foam but positioned in juxtaposition to the outer surface 34thereof. It should be noted that even though the rearmost and forwardsegments 28 and 30, respectively, have a cylindrical portion 35 whichflares radially outwardly through a transitional shoulder 36 ofprogressively increasing diameter to a bell portion 38 of greaterdiameter than the cylindrical portion 35, the sleeve 33 is adjacent theentire radially outer surface 34 of both tube segments.

The foam 32 found most suitable for use in ignition tubes is rigidpolyurethane. Rigid urethane foams may be readily produced by either oftwo methodsthe quasiprepolymer or the one shot method.

In the quasi-prepolymer method the diisocyanate is reacted with aportion of the polyester to give a NCO- ter-minated prepolymer. In thefoaming step the prepolymer is reacted with the rest of the polyester,catalyst, surfactant and fluorocarbon.

The one shot process is more economical in that no preaction step isrequired. This process requires, simply, that at least two conduits leadto the mixing head since all the components can be premixed except forthe diisocyanate. One apparatus particularly adapted for the charging ofmolds according to the one shot 4 process can be found in my UnitedStates Patent No. 3,264,067.

Properly to reinforce the tube, it has been found that a non-puckeringsleeve 33 should be incorporated. Moreover, the sleeve should be of aloose weavei.e., an open weave with interstices between parallelstrands. An open weave is more suitable for the provision of theperforations 31 without the necessity of severing the strands 39.

An open Weave is also eminently suitable for the sleeve 33 because sucha weave provides a very high adhesion strength between the sleeve 33 andthe rigid foam 32. Inasmuch as the foam penetrates the intersticesbetween the strands while it is foaming, the sleeve is encased in anhomogenous mass of rigid foam.

At least for some sizes of ignition tube the mechanical bonding of thefoam through the interstices of the sleeve 33 is sufiicient to reinforcethe tube. However, should additional bonding be required, the materialfrom which the strands are made may itself be roughened to provide anadditional mechanical bonding between the foam and the sleeve.Additionally, when little or no chemical bonding obtains between thestrand material and the foam, it may be desirable, for someapplications, to treat the sleeve with a cement to create a bond betweenthe strand material and the foam.

A weave which conforms well even to a belled tube, such as the segments28 and 30, without puckering is shown in greater detail in FIG. 4.Strands 39R are helically disposed with respect to the longitudinal axis37 of the sleeve 33 and are of right hand lay as viewed in FIG. 4. Thestrands 39R are intertwined with strands 39L, also helically disposed,of left hand lay. The strands 39R are each formed from two filaments 40and 41, and the strands 39L are each formed from two filaments 42 and43.

The two filaments in each strand 39R and 39L intersect each other in aplain weave-e.g., filament 40 in strand 39R passes over filament 42 andunder filament 43 in strand 39L while filament 41 in strand 39R passesunder filament 42 and over filament 43 of strand 39L. The aforesaidintertwining of each strand 39R and 39L forms an intersection 44.

Between consecutive intersections the two filaments in the strands ofeach lay are themselves crossed, as at changeover points 45.

Such a weave is quite stable and yet will conform exactly to the contourof the outer surface 34, even when of progressively varied diameter,without puckering. Nonpuckering results because a sleeve so woven willexpand radially upon axial compression and radially contract upon axialelongation.

Because it is imperative that the cartridge sack and its contents beconsumed in firing, the material from which lthe sleeve is woven mustnot leave a hard ash or other residue which could impair the insertionof the subsequent projectile.

Filaments 40-40, inclusive, of linear, high polymer polyesters have beenfound to leave no undesirable residue on firing. Polyester is the namegiven to the material produced by a process involving the esterificationcondensation of dihydn'c alcohols and dicarboxylic acids.

This reaction covers a broad range of materials but it is sufficient tonote that the linear, high polymer polyester ethylene glycolterephthalate, commonly known as Dacron, works exceedingly well.

The unique suitability of using a sleeve woven as shown and described inconjunction with FIG. 4 can be particularly appreciated when the methodby which the ignition tubes are made is known. As shown in FIG. 5, amold 50 is provided with a belled cavity 51 having the shape desired forthe radially outer surface of the ignition tube body, or, if theignition tube is segmented, a belled segment body.

A section 53 of woven sleeving having a diameter less than the smallestdiameter of the cavity 51 so that it is readily insertable therein iswoven to, or cut to, a length greater than the axial extent of thecavity. Such a section 53 is depicted inserted in cavity 51 in FIG. 5.With the section 53 thus inserted it is axially compressed within thecavity until the section 53 has expanded sufficiently to adapt to andlie contiguously with the surface of the cavity. With very littleexperimentation a worker is able to select a section length which willexactly equal the axial extent of the cavity after it has been expandedto conform to the surfaces thereof.

As shown in FIG. 6, the insertion of a core 54 into the mold cavity mayitself provide the compression of the section 53 as well as define theinterior of the tube to be formed in the mold. With the sleeve section53 thus expanded within the mold, the foaming of the foam formingcomponents charged into the mold creates the body of the ignition tubewith the reinforcing sleeve encased in juxtaposition with the outersurface thereof.

It should therefore be apparent that the objects of the invention havebeen accomplished.

What is claimed is:

1. An ignition tube for munitions comprising, a hollow, generallytubular, rigid foam body having a radially outer surface, a portion ofwhich is of a progressively varied diameter, a Woven, reinforcing sleeveencased in said body, the weave of said sleeve having helically orientedstrands of right hand lay intertwined with helically oriented .strandsof left hand lay so that said sleeve is compressible axially to agreater extent where the diameter of the outer surface of the bodyportion in creases to maintain the sleeve in juxtaposition with theradially outer surface of said tube.

2. An ignition tube, as set forth in claim 1, in which the helicalstrands of each lay are spaced apart and each strand is comprised of twofilaments, the two filaments in each strand of right hand layintersecting the two filaments in each strand of left hand lay in asquare weave with the two filaments in the strands of each laythemselves crossing between each intersection.

3. An ignition tube, as set forth in claim 2, in which the rigid foam ispolyurethane and the filament is a polyester.

4. An ignition tube having a rigid foam body portion, said body portionbeing at least in part a hollow cylinder with a radially outer surface,a portion of which flares radially outwardly to form a bell, andincluding a reinforcing sleeve, the improvement comprising, a wovenreinforcing sleeve, said weave being a plurality of helically orientedpolyester strands of left and right hand lay, each strand beingcomprised of two filaments, the two filaments in each strand of righthand lay intersecting the two filaments in each strand of left hand layin a plain weave with the two filaments in the strands of each laythemselves crossing between each intersection, and the sleeve beingcompressed axially to a greater degree through said bell to conform tothe greater radial dimension, said sleeve thereby maintainingjuxtaposition with the radially outer surface of said tube.

5. An ignition tube, as set forth in claim 4, in which the rigid foam ispolyurethane and the filaments are a polyester monofilament.

References Cited UNITED STATES PATENTS 2,239,051 4/1941 Pearsall et al.102-27 2,498,050 2/1950 Selvidge 102-27 3,241,489 3/1966 Andrew et al.102-27 3,257,948 6/1966 Axelrod et a1. 102-43 3,260,201 7/1966 Kelly etal. 102--27 3,263,613 8/1966 Rice et al. 861 X 3,093,160 6/1963 Boggs.

BENJAMIN A. BORCHELT, Primary Examiner.

G. H. GLANZMAN, Assistant Examiner.

